As lasers are used in increasing numbers throughout society, human beings run the risk of being exposed to harmful levels of laser radiation. Laser devices can generate radiation at a number of different wavelengths which can be either visible or invisible to the human eye. As a result, it can be difficult to know when potentially harmful levels of radiation are present in the environment.
The effects of exposure to harmful levels of laser radiation are well known and include mild to severe skin burns. In addition, laser radiation can cause serious eye injury by damaging the cornea, retina, and lens. Different wavelengths of laser radiation are associated with different types of eye injury. For example, ultraviolet radiation may cause lens damage such as cataracts, whereas exposure to infrared radiation often results in retinal and corneal burns.
The propensity of laser radiation to cause eye damage is often expressed as a function of its wavelength and time. Along these lines, safety standards such as the American National Standards Institute (ANSI) Z136 set maximum permissible exposure (MPE) limits according to the wavelength of the laser and the duration of the exposure. One exposure level, for example, relates to the human aversion time for bright-light stimuli. In other words, how much exposure can be tolerated in the time it takes to blink. Other exposure levels may be used where the blink reflex is not applicable such as with infrared radiation.
Conventional approaches to laser eye safety have relied upon the ability of protective eyewear to absorb all or part of the laser radiation before it reaches the eye. Laser safety eyewear (LSE) is thus rated according to its optical density, or the amount of the incident laser radiation at a specified wavelength that can pass through to the unprotected eye. For added protection, safety standards usually define hazard zones within which LSE devices must be used and require the use of warning signs and physical barriers within each hazard zone.
Unfortunately, strict adherence to safety standards is not always possible. For example, military personnel may be exposed to high-powered lasers on the battlefield without knowing the type of laser involved and exposure may occur in situations where the use of cumbersome eye protection is not an option. Similarly, malicious use of laser devices may create serious hazards to aviation and maritime personnel using high-powered optics to monitor the passage of planes, ships, etc. Therefore, there is a need for improved protection against harmful levels of radiation.